1. Field of the Invention
The subject invention generally relates to a compression transmission collar apparatus for fastening two members. The subject invention is specifically applicable to a compression transmission collar apparatus that is implantable into bone for use in treating bone factures by skeletal fixation medical procedures.
2. Description of the Prior Art
Skeletal fixation is a well known type of medical procedure for treating bone factures. The skeletal fixation procedures known in the art typically call for the use of fasteners to fixate, or fasten, the ends of the fractured bone to one another. Accordingly, the fasteners and other related hardware used in typical skeletal fixation procedures are analogous to the fasteners and other related hardware used in other applications such as carpentry, construction, and assembly.
U.S. patent application Ser. No. 12/818,395 to LeCronier et al. teaches an easily implantable and stable nail-fastener apparatus for skeletal fixation including an intramedullary nail for insertion into the medullary canal of a bone. The intramedullary nail defines a threaded bore extending transverse to the intramedullary nail. A threaded fastener including a threaded portion extending transversely to the intramedullary nail threadedly engages the bore of the intramedullary nail. A compression transmission collar of annular shape having an exterior face and a top edge is provided for receiving a compressional load from the threaded fastener and transmitting the compressional load to the intramedullary nail. When simplified to the more general field of fasteners, the bone essentially comprises a first member defining a hole having a hole wall and the intramedullary nail comprises a second member defining a threaded bore. A threaded fastener then is provided to threadedly engage the bore and fixate the first member to the second member. Lastly, a compression transmission collar of annular shape is provided to transmit the compressional load of the fastener to at least one of the fastened members.
One compression transmission collar well known in the art of fasteners and related hardware is the helical lock washer. Expired U.S. Pat. No. 1,655,018 to Loutrel teaches a compression spring washer for use with fasteners. The Loutrel design discloses a helical shaped washer having a top edge and a bottom edge and a first end and a second end defining a slit. The top edge is designed to contact the threaded fastener for receiving a compressional load from the threaded fastener and the bottom edge is design to contact and transmit the compressional load to one of the fastened members. Finally, due to the helical shape of the Loutrel design, the compression spring washer has an extended length and a compressed length.
A problem with the compression transmission collars known in the art, such as the helical lock washer, is that the compressional load received by the compression transmission collar is transmitted axially to the surface of the fastened member surrounding the hole or the bore. Axial transmission of the compressional load in close proximity to the hole or bore is particularly problematic where at least one of the fastened members is a brittle or easily deformable material. In such cases, the axial transmission of the compressional load can easily cause the material to break, crack, or deform because it has already been weakened by the presence of the hole or bore. This problem is especially significant in skeletal fixation procedures because they involve the repair of an already fractured bone which is a brittle material. Accordingly, there remains a need for a compression transmission collar that provides for the fastening of two members but does not transmit a compressional load to one of the fastened members in the axial direction.